Pathways for the Formation of C₂₊ Products under Alkaline Conditions during the Electrochemical Reduction of CO₂

Abstract

Establishing how Cu facilitates the electrochemical CO 2 reduction reaction (CO2RR) to C 2+ products remains a critical challenge. Under typical reaction conditions, the pH near the electrode is considerably more alkaline than that in the bulk due to mass transport limitations. Challenges with probing alkaline pathways using computational methods have limited understanding of the CO2RR under experimentally relevant conditions. In this work, using the Volmer reaction on Cu (100), we demonstrate that predicted activation barriers can substantially differ between acidic and alkaline pathways. We compute reaction energetics for alkaline *CO protonation and find that, while the formation of *CHO is preferred thermodynamically, the formation of *COH is favored kinetically at high overpotential. However, we find formation of *CHO via reaction of *H and *CO feasible at room temperature. We report potential-dependent energetics for forming the first C−C bond in CO2RR and find that CO dimerization likely dominates. Finally, we investigate how long-range van der Waals interactions impact our results by comparing to the meta-GGA B97M-rV.

Electrochemical Hydrogenation of CO on Cu(100): Insights from Accurate Multiconfigurational Wavefunction Methods

“…conditions on Cu(100) and predicted that high overpotentials favor *COH formation while low overpotentials favor *CHO formation. 24 The same authors further suggested that CO dimerization likely dominates C−C bond formation steps. 24 The above-mentioned theoretical studies all used various pure DFT approximations, which suffer from electron selfinteraction error and incorrect frontier−orbital or band gaps, resulting in spuriously facile charge transfer.…”

“…24 The same authors further suggested that CO dimerization likely dominates C−C bond formation steps. 24 The above-mentioned theoretical studies all used various pure DFT approximations, which suffer from electron selfinteraction error and incorrect frontier−orbital or band gaps, resulting in spuriously facile charge transfer. 25 This is worrisome for modeling heterogeneous (electro)catalysis; 26−28 with respect to the particular electrocatalyst of interest here, pure DFT does not even correctly predict the adsite preference of the key catalytic intermediate (*CO) in CO 2 R on Cu surfaces.…”

“…Previously, both Luo et al and Cheng et al used DFT-PBE to predict low applied potentials (−0.4 V vs the RHE and −0.5 V vs the RHE, respectively) for *CO hydrogenation to produce *CHO on Cu(100); these values are similar to our predicted onset potentials, although we predict instead a preference for *COH formation. By contrast, Goodpaster et al suggested a high applied potential (−1.0 V vs the RHE) for *CO hydrogenation to form *CHO on the same facet using DFT-RPBE, and Gauthier et al obtained an even more negative applied potential (U < −1.2 V vs the RHE) to form *COH using DFT-RPBE. In addition to the differences in the XC functionals the authors used in these previous DFT studies of *CO hydrogenation on Cu(100), the authors also undertook different approaches to replicate the experimental electrochemical environment with regard to imposing constant potential condition, water solvation, and pH.…”

“…Luo et al confirmed the same CO hydrogenation step but found a different C–C coupling mechanism involving two *CHOs at relatively low overpotentials (−0.4 to −0.6 V vs the RHE) on Cu(100), using DFT-PBE . Gauthier et al recently used DFT-RPBE to examine CO hydrogenation under alkaline conditions on Cu(100) and predicted that high overpotentials favor *COH formation while low overpotentials favor *CHO formation . The same authors further suggested that CO dimerization likely dominates C–C bond formation steps …”

“…Gauthier et al recently used DFT-RPBE to examine CO hydrogenation under alkaline conditions on Cu(100) and predicted that high overpotentials favor *COH formation while low overpotentials favor *CHO formation . The same authors further suggested that CO dimerization likely dominates C–C bond formation steps …”